TO TURN OR NOT TO TURN: THAT IS THE QUESTION
What is one of the first things to come to mind when one thinks of compost? Turning the pile. Turn, turn, turn, has become the mantra of composters worldwide. Early researchers who wrote seminal works in the composting field, such as Gotaas, Rodale, and many others, emphasize turning compost piles, almost obsessively so.
Much of compost's current popularity in the West can be attributed to the work of Sir Albert Howard, who wrote An Agricultural Testament (1943) and several other works on aspects of what has now become known as organic agriculture. Sir Howard's discussions of composting techniques focus on the Indore process of composting, a process developed in Indore, India, between the years of 1924 and 1931. The Indore process was first described in detail in Sir Howard's work (co-authored with Y. D. Wad), The Waste Products of Agriculture, in 1931. The two main principles underlying the Indore composting process include: 1) mixing animal and vegetable refuse with a neutralizing base, such as agricultural lime; and 2) managing the compost pile by physically turning it. The Indore process subsequently became adopted and espoused by composting enthusiasts in the West, and today one still commonly sees people turning and liming compost piles. For example, Robert Rodale wrote in the February, 1972 issue of Organic Gardening concerning composting humanure, "We recommend turning the pile at least three times in the first few months, and then once every three months thereafter for a year."
A large industry has emerged from this philosophy, one which manufactures expensive compost turning equipment, and a lot of money, energy, and expense goes into making sure compost is turned regularly. To some compost professionals, the suggestion that compost doesn't need to be turned at all is utter blasphemy. Of course you have to turn it - it's a compost pile, for heaven's sake.
Or do you? Well, in fact, NO, you don't, especially if you're a backyard composter, and not even if you're a large scale composter. The perceived need to turn compost is one of the myths of composting.
Turning compost potentially serves four basic purposes. First, turning is supposed to add oxygen to the compost pile, which is supposed to be good for the aerobic microorganisms. We are warned that if we do not turn our compost, it will become anaerobic and smell bad, attract rats and flies, and make us into social pariahs in our neighborhoods. Second, turning the compost ensures that all parts of the pile are subjected to the high internal heat, thereby ensuring total pathogen death, and yielding a hygienically safe, finished compost. Third, the more we turn the compost, the more it becomes chopped and mixed, and the better it looks when finished, rendering it more marketable. Fourth, frequent turning can speed up the composting process. Since backyard composters don't actually market their compost, usually don't care if it's finely granulated or somewhat coarse, and usually have no good reason to be in a hurry, we can eliminate the last two reasons for turning compost right off the bat. Let's look at the first two.
Aeration is necessary for aerobic compost, which is what we want. There are numerous ways to aerate a compost pile. One is to force air into or through the pile using fans, which is common at large-scale composting operations, where air is sucked from under the compost piles and out through a biofilter. The suction causes air to seep into the organic mass through the top, thereby keeping it aerated. However, this air flow is more often than not a method for trying to reduce the temperature of the compost, because the exhaust air draws quite a bit of heat away from the compost pile. Mechanical aeration is never a need of the backyard composter, and is limited to large scale composting operations where the piles are so big they can smother themselves if not subjected to forced aeration.
Aeration can also be achieved by poking holes in the compost, driving pipes into it, and generally impaling it. This seems to be popular among some backyard composters. A third way is to physically turn the pile. A fourth, largely ignored way, however, is to build the pile so that tiny interstitial air spaces are trapped in the compost. This is done by using coarse materials in the compost, such as hay, straw, weeds, and the like. When a compost pile is properly constructed, no additional aeration will be needed. Even the organic gardening pros admit that, "good compost can be made without turning by hand if the materials are carefully layered in the heap which is well-ventilated and has the right moisture content." 45
This is especially true for "continuous compost," which is different from "batch compost." Batch compost is made from a batch of material that is composted all at once. This is what commercial composters do - they get a dumptruck load of garbage or sewage sludge from the municipality and compost it in one big pile. Backyard composters, especially humanure composters, produce organic residues daily, a little at a time, and rarely, if ever, in big batches. Therefore, continuous composters add material continuously to a compost pile, usually by putting the fresh material on the top. This causes the thermophilic activity to be in the upper part of the pile, while the thermophilically "spent" part of the compost sinks lower and lower to be worked on by fungi, actinomycetes, earthworms, and lots of other things. Turning continuous compost dilutes the thermophilic layer with the spent layers and can quite abruptly stop all thermophilic activity.
Researchers have measured oxygen levels in large-scale windrow composting operations (a windrow is a long, narrow pile of compost). One reported, "Oxygen concentration measurements taken within the windrows during the most active stage of the composting process, showed that within fifteen minutes after turning the windrow - supposedly aerating it - the oxygen content was already depleted." 46 Other researchers compared the oxygen levels of large, turned and unturned batch compost piles, and have come to the conclusion that compost piles are largely self-aerated. "The effect of pile turning was to refresh oxygen content, on average for [only] 1.5 hours (above the 10% level), afterwhich it dropped to less than 5% and in most cases to 2% during the active phase of composting . . . Even with no turning, all piles eventually resolve their oxygen tension as maturity approaches, indicating that self-aeration alone can adequately furnish the composting process . . . In other words, turning the piles has a temporal but little sustained influence on oxygen levels." These trials compared compost that was not turned, bucket turned, turned once every two weeks, and turned twice a week.47
Interestingly enough, the same trials indicated that bacterial pathogens were destroyed whether the piles were turned or unturned, stating that there was no evidence that bacterial populations were influenced by turning schemes. There were no surviving E. coli or Salmonella strains, indicating that there were "no statistically significant effects attributable to turning." Unturned piles can benefit by the addition of extra coarse materials such as hay or straw, which trap extra air in the organic material and make additional aeration unnecessary. Furthermore, unturned compost piles can be covered with a thick insulating layer of organic material, such as hay, straw, or even finished compost, which will allow the temperatures on the outer edges of the pile to warm enough for pathogen destruction.
Not only can turning compost piles be an unnecessary expenditure of energy, but the above trials also showed that when batch compost piles are turned frequently, some other disadvantageous effects can result (see Figure 3.6). The more frequently compost piles are turned, the more they lose agricultural nutrients. When the finished compost was analyzed for organic matter and nitrogen loss, the unturned compost showed the least loss. The more frequently the compost was turned, the greater was the loss of both nitrogen and organic matter. Also, the more the compost was turned, the more it cost. The unturned compost cost $3.05 per wet ton, while the compost turned twice a week cost $41.23 per wet ton, a 1,351% increase. The researchers concluded that "Composting methods that require intensification [frequent turning] are a curious result of modern popularity and technological development of composting as particularly evidenced in popular trade journals. They do not appear to be scientifically supportable based on these studies . . . By carefully managing composting to achieve proper mixes and limited turning, the ideal of a quality product at low economic burden can be achieved." 48 Backyard composters like the "low economic burden" part of that statement.
When large piles of compost are turned, they give off emissions of such things as Aspergillus fumigatus fungi, which can cause health problems in people. Aerosol concentrations from static (unturned) piles are relatively small when compared to mechanically turned compost. Measurements thirty meters downwind from static piles showed that aerosol concentrations of A. fumigatus were not significantly above background levels, and were "33 to 1800 times less" than those from piles that were being moved.49
Finally, turning compost piles in cold climates can cause them to lose too much heat. It is recommended that cold climate composters turn less frequently, if at all.50
DO YOU NEED TO INOCULATE YOUR COMPOST PILE?
No. This is perhaps one of the most astonishing aspects of composting. In October of 1998, I took a trip to Nova Scotia, Canada, to observe the municipal composting operations there. The Province had legislated that as of November 30, 1998, no organic materials could be disposed of in landfills. By the end of October, with the "ban date" approaching, virtually all municipal organic garbage was being collected and transported instead to composting facilities, where it was effectively being recycled and converted into humus. The municipal garbage trucks would simply back into the compost facility building (the composting was done indoors), and then dump the garbage on the floor. The material consisted of the normal household and restaurant food materials such as banana peels, coffee grounds, bones, meat, spoiled milk, and paper products such as cereal boxes. The occasional clueless person would contribute a toaster oven, but these were sorted out. The organic material was then checked for other contaminants such as bottles and cans, run through a grinder, and finally shoved into a concrete compost bin. Within 24-48 hours, the temperature of the material would climb to 70°C (158°F). No inoculants were required. Incredibly, the thermophilic bacteria were already there, waiting in the garbage for this moment to arrive.
Researchers have composted materials with and without inocula and found that, "although rich in bacteria, none of the inocula accelerated the composting process or improved the final product . . . The failure of the inocula to alter the composting cycle is due to the adequacy of the indigenous microbial population already present and to the nature of the process itself . . . The success of composting operations without the use of special inocula in the Netherlands, New Zealand, South Africa, India, China, the USA, and a great many other places, is convincing evidence that inocula and other additives are not essential in the composting of [organic] materials." 51 Others state, "No data in the literature indicate that the addition of inoculants, microbes, or enzymes accelerate the compost process." 52
It is not necessary to put lime (ground agricultural limestone) on your compost pile. The belief that compost piles should be limed is a common misconception. Nor are other mineral additives needed on your compost. If your soil needs lime, put the lime on your soil, not your compost. Bacteria don't digest limestone; in fact lime is used to kill microorganisms in sewage sludge (lime-stabilized sludge).
Aged compost is not acidic, even with the use of sawdust. The pH of finished compost should slightly exceed 7 (neutral). What is pH? It's a measure of acidity and alkalinity which ranges from 1-14. Neutral is 7. Below seven is acidic, above seven is basic or alkaline (see Figure 3.7). If the pH is too acidic or too alkaline, bacterial activity will be hindered or stopped completely. Lime and wood ashes raise the pH, but wood ashes should also go straight on the soil. The compost pile doesn't need them. It may seem logical that one should put into one's compost pile whatever one also wants to put into one's garden soil, as the compost will end up in the garden eventually, but that's not the reality of the situation. What one should put into one's compost is what the microorganisms in the compost want or need, not what the garden soil wants or needs.
Sir Albert Howard, one of the most well-known proponents of composting, as well as J. I. Rodale, another prominent organic agriculturist, have recommended adding lime to compost piles.53 They seemed to base their reasoning on the belief that the compost will become acidic during the composting process, and therefore the acidity must be neutralized by adding lime to the pile while it's composting. It may well be the case that some compost becomes acidic during the process of decomposition, however, it seems to neutralize itself if left alone, yielding a neutral, or slightly alkaline end product. Therefore, it is recommended that you test your finished compost for pH before deciding that you need to neutralize any acids.
I find it perplexing that the author who recommended liming compost piles in one book, states in another, "The control of pH in composting is seldom a problem requiring attention if the material is kept aerobic. . . the addition of alkaline material is rarely necessary in aerobic decomposition and, in fact, may do more harm than good because the loss of nitrogen by the evolution of ammonia as a gas will be greater at the higher pH."54 In other words, don't assume that you should lime your compost. Only do so if your finished compost is consistently acidic, which would be highly unlikely. Get a soil pH test kit and check it out. Researchers have indicated that maximum thermophilic composting occurs at a pH range between 7.5 to 8.5, which is slightly alkaline.55 But don't be surprised if your compost is slightly acidic at the start of the process. It should turn neutral of slightly alkaline and remain so when completely cured.
According to a 1991 report, scientists who were studying various commercial fertilizers found that agricultural plots to which composted sewage sludge had been added made better use of lime than plots without composted sludge. The lime in the composted plots changed the pH deeper in the soil, indicating that organic matter assists calcium movement through the soil "better than anything else," according to Cecil Tester, Ph.D., research chemist at USDA's Microbial Systems Lab in Beltsville, MD.56 The implications are that compost should be added to the soil when lime is added to the soil.
Perhaps Gotaas sums it up best, "Some compost operators have suggested the addition of lime to improve composting. This should be done only under rare circumstances such as when the raw material to be composted has a high acidity due to acid industrial wastes or contains materials that give rise to highly acid conditions during composting." 57
WHAT NOT TO COMPOST? YOU CAN COMPOST ALMOST ANYTHING
I get a bit perturbed when I see compost educators telling their students that there is a long list of things "NOT to be composted!" This prohibition is always presented in such an authoritative and serious manner that novice composters begin trembling in their boots at the thought of composting any of the banned materials. I can imagine naive composters armed with this misinformation carefully segregating their food scraps so that, god forbid, the wrong materials don't end up in the compost pile. Those banned materials include meat, fish, dairy products, butter, bones, cheese, lard, mayonnaise, milk, oils, peanut butter, salad dressing, sour cream, weeds with seeds, diseased plants, citrus peels, rhubarb leaves, crab grass, pet manures, and, perhaps worst of all: human manure. Presumably, one must segregate half-eaten peanut butter sandwiches from the compost bucket, or any sandwich with mayonaisse or cheese, or any left-over salad with salad dressing, or spoiled milk, or orange peels, all of which must go to a landfill and be buried under tons of dirt instead of being composted. Luckily, I was never exposed to such instructions, and my family has composted EVERY bit of food scrap it has produced, including meat, bones, butter, oils, fat, lard, citrus peels, mayonnaise, and everything else on the list; we've done this in our backyard for almost 25 years with never a problem. Why would it work for me and not for anyone else? The answer, in a word, if I may hazard a guess, is humanure, another forbidden compost material.
When compost heats up, much of the organic material is quickly degraded. This holds true for oils and fats, or in the words of scientists, "Based on evidence on the composting of grease trap wastes, lipids [fats] can be utilized rapidly by bacteria, including actinomycetes, under thermophilic conditions." 58 The problem with the materials on the "banned" list, is that they do require thermophilic composting conditions for best results. Otherwise, they can just sit in the compost pile and only very slowly decompose. In the meantime, they can look very attractive to the wandering dog, cat, raccoon, or rat. Ironically, when the forbidden materials, including humanure, are combined with other compost ingredients, thermophilic conditions will prevail. When humanure and the other controversial organic materials are segregated from compost, thermophilic conditions may not occur at all. This is a situation that is probably quite common in most backyard compost piles. The solution is not to segregate materials from the pile, but to add nitrogen and moisture, as is commonly found in manure.
As such, compost educators would provide a better service to their students if they told them the truth: almost any organic material will compost, rather than give them the false impression that some common food materials will not. Granted, some things do not compost very well. Bones are one of them, but they do no harm in a compost pile.
Nevertheless, toxic chemicals should be kept out of the backyard compost pile. Such chemicals are found, for example, in "pressure treated" (i.e. poison-soaked) lumber, which is saturated with cancer-causing chemicals (chromated copper arsenate). What not to compost: sawdust from pressure treated lumber, which is, unfortunately, a toxic material that is more and more available to the average gardener.
Source: The Humanure Handbook. Jenkins Publishing,
PO Box 607, Grove City, PA 16127. To order, phone: 1-800-639-4099.